1. Field of the Invention
The present invention relates to photothermographic dry silver elements containing color forming developers.
2. Prior Art
Photosensitive, heat-developable, dry silver sheet materials, as described for example in U.S. Pat. Nos. 3,457,075 and 3,839,049, contain a photosensitive silver halide catalyst-forming means in catalytic proximity with a heat sensitive combination of a light stable organic silver compound and a reducing agent therefor. When struck by light, the silver halide catalyst-forming means produces silver nuclei which serve to catalyze the reduction of the organic silver compound, e.g., silver behenate, by the reducing agent at elevated temperatures. To improve the image density and color it has been found desirable to include toners in the sheet construction.
Color photothermographic imaging systems have been described in patent literature. U.S. Pat. No. 3,531,286 describes a system using paraphenylenediamine and photographic color couplers. U.S. Pat. No. 3,985,565 discloses the use of phenolic leuco dye reducing agents to reduce the silver and provide a color image. U.S. Pat. No. 4,460,681 discloses a multilayer color photothermographic system using a variety of leuco dyes separated by barrier layers.
U.S. Pat. No. 3,873,340 describes a pressure-sensitive copying paper comprising an encapsulated phenoxazine compound generically inclusive of some of the developers described in the present invention.
U.S. Pat. No. 4,370,401 describes a photosensitive, thermally developable imaging system which contains leuco dyes. At least one of the described leuco dyes is within the scope of developers recited in the present invention.
Japanese Patent Publication 47-4638 (1972) referenced in Chemical Abstracts, 40-Dyes, Vol. 77, 1972, 21570r describes thiazine dyes including N-[arylsulfonyl] phenothiazines as color formers in pressure sensitive papers.